Reticle for use in a guidance seeker for a spinning projectile

ABSTRACT

A reticle for a guidance seeker for spinning projectiles comprises a substrate; a pattern of a plurality of alternating light modulating structures, such as opaque and light transmitting, or light absorbing and light reflecting areas on the substrate such that an image of a target moving on the substrate will generate a plurality of pulses corresponding to the number of lines crossed by the image, the number of pulses increasing as the image moves outwardly from the center of the reticle; and a distinguishable, unambiguous, and singly periodic feature of the pattern, which is readily detectable every time the target image moves circumferentially, completing a full circle around the center of the reticle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.09/002,370, filed Jan. 2, 1998 now U.S. Pat. No. 6,076,765, and claimsthe benefit of U.S. patent applications Ser. No. 60/047,476, filed May23, 1997 and U.S. Patent Applications Ser. No. 60/034,006, filed Jan. 2,1997, the disclosures of which applications are incorporated byreference in their entirities herein.

FIELD OF THE INVENTION

The present invention pertains generally to guidance seekers forspinning projectiles and specifically to a guidance seeker utilizing areticle for determining the instantaneous target location relative tothe projectile's spin axis.

BACKGROUND OF THE INVENTION

The present invention is related to applicant's U.S. Pat. No. 5,529,262,which is hereby incorporated by reference. The present invention is alsorelated to provisional applications, Ser. Nos. 60/034,006 and60/047,476; filed Jan. 2, 1997 and May 23, 1997, respectively, which areincorporated herein by reference.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a guidance seekerfor spinning projectiles that uses the projectile inertial properties asa guidance reference.

It is another object of the present invention to provide a guidanceseeker with no moving parts.

It is still another object of the present invention to provide aguidance seeker of relatively very low cost, and small size and weightrealization, thereby making it particularly suitable for very smallcaliber spinning projectile applications.

It is another object of the present invention to provide a guidanceseeker for spinning projectiles that can be implemented together withall necessary electronic circuitry on a single silicon chip.

It is yet another object of the present invention to provide a guidanceseeker that is suitable for a wide variety of small projectileapplications, from handgun projectiles to artillery to small tacticalmissiles.

In summary, the present invention provides a reticle for a guidanceseeker for a spinning projectile comprising a substrate for beingsecured stationary with the spinning projectile; a pattern of aplurality of alternating light modulating structures, such as opaque orlight absorbing and light transmitting or light reflecting areasrespectively on the substrate, such that an image of a target moving onthe substrate in a cyclical fashion will generate (1) a plurality ofpulses corresponding to the number of such light transmitting or lightreflecting areas crossed by the image, the number of pulses increasingover the spin cycle as the image moves outwardly from the center of thereticle; and (2) the pulse lengths and/or the interstitial time periodsbetween pulses vary in a unique, distinguishable, unambiguous, andsingly periodic fashion during the spin cycle. Opaque and lighttransmitting pertain to refractive optics realizations, while lightabsorbing and light reflecting pertain to reflective optics. Bothembodiments are essentially equivalent in principle, but one or theother may be more advantageous for realization depending on the spectralregion of operation.

These and other objects of the present invention will become apparentfrom the following detailed description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a reticle with a chevron-shaped pattern made in accordancewith the present invention.

FIG. 2A is a schematic perspective view of the reticle based onrefractive optics embodiment of the present invention disposed inside aprojectile equipped with divert thrusters used for course correction.

FIG. 2B is a schematic perspective view of a reticle based on reflectiveoptics embodiment of the present invention disposed inside theprojectile FIG. 2A.

FIG. 2C is a schematic side view of the embodiment of FIG. 2B, showingthe reticle integrated with the condenser mirror and using reflectiveand absorbing reticle pattern.

FIG. 3 is an exemplary signal generated by the reticle of the presentinvention.

FIG. 4 is yet another embodiment of a reticle made in accordance withthe present invention.

FIG. 5 is an exemplary signal generated by the reticle of FIG. 4.

FIG. 6 is yet another embodiment of a reticle made in accordance withthe present invention.

FIGS. 7A, 7B and 7C are illustrative signals generated by the reticle ofFIG. 6 from three different point targets.

FIG. 8 is yet another embodiment of a reticle made in accordance withthe present invention.

FIG. 9 is still another embodiment of a reticle made in accordance withthe present invention.

FIG. 10 is a functional block diagram of a signal processing circuitused to extract the signal from the reticle of FIG. 6.

FIG. 11 is a functional block diagram of the phaselock loop circuitblock of FIG. 10.

FIG. 12 is an exemplary circuit that may be used for processing thesignal generated by a reticle of the present invention.

FIGS. 13A, 13B, 13C and 13D are waveforms generated at various points inthe circuit of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

A reticle R in accordance with the present invention is disclosed inFIG. 1. For the refractive optics embodiment, the reticle R includes alight modulating structure made of a plurality of alternatingchevron-shaped opaque lines 2 alternating with light transmitting spaces4 therebetween and a blank light transmitting sector 6. For a reflectiveoptics embodiment, there would be alternating light absorbing and lightreflecting regions corresponding to the opaque lines 2 an transmittingspaces 4.

The reticle R is secured to a projectile such that it has no relativemotion with respect to the projectile. The reticle R is rotated aboutits center 8 from the spinning motion of the projectile. The pattern oflines of reticle R is advantageously designed such that a circle drawnabout the center 8 by the point image of a target will intersect anincreasing number of lines 2 as the radius of the circle increases toprovide information on the deviation of the line-of-sight to the targetfrom the projectile, as illustrated by the circles 10, 12 and 14.

The reticle R is implemented, for the refractive optics embodiment, on asubstrate which would allow light, infra-red or other radiation that isemitted by or reflected from the target to pass through to aphotodetector and be interrupted periodically in accordance with thepattern of light modulating structures of opaque and light transmittingregions. For the reflective optics embodiment, the substrate could beeither light transmitting, as in the refractive embodiment, or lightreflecting such as a polished metal surface which would carry a similarpattern of light absorbing or nonreflecting regions corresponding to theopaque lines 2. Yet another possibility for this embodiment would be anonreflecting substrate carrying a pattern of reflecting regions. Ineither case, the light or infra-red energy impinging onto a suitabledetector would be periodically interrupted in a similar fashion as inthe refractive optics embodiment.

The reticle R is placed in the image plane of an objective lens 16, oran objective primary mirror 17 as best shown in FIGS. 2A and 2B,respectively. Both are placed inside a spinning projectile 18 such thatthe reticle R is secured stationary with respect to the projectile, withthe optical axis 20 of the lens 16 and the reticle R coinciding with theprojectile spin axis, as best shown in FIG. 2A. The same is true for thereflective embodiment, where the optical axis of the objective mirror 17and the center of the reticle R are aligned with the spin axis of theprojectile, as best shown in FIG. 2B. Rotation, in both cases, isimparted to the reticle R by virtue of the projectile spin, since thereis no relative motion between the reticle R and the projectile. Acondenser lens 22 focuses the light passing through the reticle to adetector 24, such as a photodetector or an infra-red detector. In thereflective case, a condenser mirror 33, or secondary mirror, fulfillsthe same function. The condenser mirror 33 could simultaneously serve asthe substrate for the reticle 35, as best shown in FIG. 2C and so couldthe condenser lens 22 mentioned above. In both cases, a circuit 26 isoperably connected to the detector 24. The circuit 26 provides forsequencing, timing and firing a divert thruster 28. The divert thruster28 is operably connected to the circuit 26 through firing leads 30. Thedivert thruster 28 is used to correct the trajectory of the projectileby affecting a lateral motion component upon activation. The reticle-R,detector 24 and the circuit 26 may be implemented on a single chip, inwhich case the condenser lens 22 would not be needed.

The operation of the reflective embodiment of the reticle will now bedescribed. A person skilled in the art will understand that theoperation of the reflective embodiment will be similar.

As the projectile 18 spins about its axis 20, the image 32 of a pointtarget 34 at a radial distance 36 from the center of the reticle, willfollow a circular path, such as the circle 10 shown in FIG. 1. As theimage crosses the reticle lines, the light from the point target ischopped by the reticle structure, and produces electronic pulse signalsat the detector 24. The target image 32 moves in the image plane due toprojectile spin, since the reticle R does not move by itself.

An illustrative signal generated by the image 32 as it traces a patharound the center of the reticle is shown in FIG. 3. The alternatingopaque and light transmitting lines 2 and 4 produce groups of signals38, one group for each complete revolution of the projectile or reticleabout the spin axis. Each group of signals consists of a plurality ofpulses, each pulse being generated each time the image 32 crosses anopaque line 2 and into a light transmitting line 4. Each group isseparated from the next group by a distinctive signal 40 generated bythe image 32 when it traverses the light transmitting area 6. The signal40 would have maximum amplitude in the case where the area 6 is lighttransmitting in the refractive embodiment or light reflecting inreflective embodiment, and minimum amplitude in the case where the area6 is opaque in the refractive example and light absorbing in thereflective embodiment. Maximum amplitude is generated when the imagefalls on the light transmitting area 6 and minimum amplitude when itcrosses an opaque line 2. The pulse count is proportional to the radialdistance 36 of the image 32 from the center 8 or spin axis 20 of theprojectile, since more opaque and light transmitting lines will becrossed by the image at a greater distance from the center. The radialdistance 36 is proportional to an angle 42 that a line-of-sight 44 tothe target 34 makes with the projectile spin axis 20, which is along thedirection of travel of the projectile, as best shown in FIG. 2A. Whenthe image moves through the blank area 6, a distinctive signal 40 isgenerated that advantageously separates each group of signals 38. Thisunique signal is used as a reference point for determining theinstantaneous angular position of the image with respect to the reticlecenter 8 or the projectile axis. The distinctive signal 40 is generatedonce every complete rotation of the reticle R.

If the target image is centered on the reticle, which means that theprojectile axis 20 and the target line-of-sight 44 are coincident, nosignals would be generated by the reticle, indicating that the target isin the direction of the projectile axis and that no correction to theprojectile course is required. However, if the target deviates from thecenter of the reticle, the lines 2 and spaces 4 will generate a seriesof pulses, indicating that the projectile is not pointed at the target.As the projectile farther deviates from the target, the number of pulsesgenerated will increase, since more lines will be crossed at a greaterdistance from the center, indicating the need for greater coursecorrection. For example, the number of pulses generated by the path 10will be smaller than either of the paths 12 and 14. Similarly, thenumber of pulses generated by the path 12 will be less than path 14. Aperson skilled in the art will understand that as the line-of-sightangle 42 gets larger, the number of pulses generated by the target imageon the reticle will also get larger. Conversely, as the line-of-sightangle 42 gets smaller, the number of pulses generated will get smaller.When the angle 42 approaches zero, then the projectile axis will belined up with the target for a hit.

The divert thruster 28, as disclosed in provisional application Ser. No.60/056,097, filed Aug. 20, 1997, which is incorporated herein byreference, includes a plurality of propellant or explosive cells 46disposed in a ring around the projectile center of mass. To correct thebearing of the projectile, a vector force impulse 48 of the appropriateamount, supplied from firing one or more of the explosive cells 46,depending on the radial distance 36, is applied through the center ofmass of the projectile along a line passing through the image 32 and thereticle center, such that the angle 42 and the radial distance 36 arereduced to zero. The distinctive signal 40 generated by the target imageat the blank sector 6 of the reticle R provides a reference point fromwhich to sequence the firing of the divert thruster 28. The clockfrequency generated by the target image moving across the lines 2 and 4of the reticle R is indicative of the spin rate of the projectile andprovides a means for sequencing the firing of each of the explosivecells 46 in the divert thruster 28. Since the timing of the distinctivesignal (when the image 32 crosses the sector 6) and the spin rate of theprojectile is known, (from these distinctive signals, and therefore alsothe clock frequency, which is an integer multiple of these distinctsignals, whereby the integer is equal to the number of divert thrustercells around the projectile) the timing for each of the explosive cells46 can be determined as to when it would be positioned along a linepassing through the image 32 and the reticle center, at which time itwould be fired to provide the vector force for course correction.

As seen from the above, the reticle R has the capability of determiningthe instantaneous target location in polar coordinates centered aboutthe projectile's spin axis. The parameters measured are theinstantaneous radial position of the target image in the image plane,and the corresponding instantaneous angle. These readily transform viathe seeker optics, into a line-of-sight angle, and a polar angle inreference to projectile orientation. The former is necessary fordetermining the course correction required, while the latter is neededto ascertain the precise timing and direction of the course correction.

Another embodiment of a reticle S in accordance with the presentinvention is disclosed in FIG. 4. The reticle S includes a plurality oflight modulating structures of opaque concentric arcs 50 alternatingwith light transmitting spaces 52 therebetween equally spaced from eachother and rotated about an axis 54. As a target image traverses thereticle plane in a circular motion as a result of the rotation of theprojectile about the optical axis, which coincides with the projectileaxis, a signal pattern similar to that shown in FIG. 5 is generated bythe sequence of intersections of the reticle lines 50 and 52 by theimage 32 and traversal through a sector area 53. The pulses 38 for eachrevolution of the reticle are separated by the unique signal 40, whichcould be a minimum or maximum, depending on whether the image happenedto fall on the line or the space. The signal pattern containsinformation regarding the angular offset 42 (angle of view) of theline-of-sight of the target from the projectile axis and the angularposition of the image on the reticle plane. Specifically, the number ofreticle lines crossed by the target image 32 is proportional to theangle of view, and the maximum time interval between reticle crossings,generally indicated at 53, generating a distinctive signal everycomplete revolution of the reticle, that occurs at the time when thetarget image path is substantially parallel to the arcs 50. These twoparameters, the number of Limes crossed and the longest interval betweenline crossings, are measurable and are necessary and sufficient forobtaining a converging guidance solution. As with the reticle R,agreater number of-pulses are generated per revolution of the reticle asthe image 32 drifts radially outwardly from the rotation axis 54,indicating that the target is drifting away from the path of theprojectile. For example, path 58 will generate more pulses than path 60,since more reticle lines will be crossed at the outer radial distances.

Another embodiment of a reticle T in accordance with the presentinvention is disclosed in FIG. 6. The reticle T consists of a widesector 62 of light modulating structures of alternating lighttransmitting and opaque narrow sectors 64 and 66, respectively. Thenarrow sectors reverse in sequence at the center 68 where there is adouble width of light transmitting narrow sector 64. The change in thesequence at 68 represents a phase jump of 180°, which provides a unique,unambiguous, detectable and singly periodic signal for each rotation ofthe reticle, advantageously providing a reference point for firing adivert thruster to correct the trajectory of the projectile.

Another wide sector 70 is provided on the reticle T and consists of aplurality of parallel opaque lines 72 of equal spacing. The parallellines 72 divide the sector 70 into alternating light transmitting andopaque portions 71 and 73, respectively.

The wide sectors 62 and 70 can be separated by semitransparent sectors74 and 76 with no structure. The unstructured sectors 74 and 76advantageously provide signal group separations in time, depending onthe signal processing requirements. Typical angular width for theunstructured sectors 74 and 76 can range from 0 to quite significantangles of 90 degrees or even greater.

The operation of the reticle T will now be described, using three pointtargets as seen by the reticle from different line-of-sight angles. Asthe projectile 18 spins about its axis, the images of the three targetswill follow circular paths 78, 80 and 82, as best shown in FIG. 6. Thelight from the point targets is thus chopped by the reticle structure,and produces electronic signals at the photodetector 24, as best shownin FIGS. 7A, 7B and 7C. Starting at A in FIG. 6, the target images moveclockwise in the image plane due to projectile spin. The wide sector 62with alternating light and opaque narrow sectors produce periodicsignals 84 with the phase jump of 180 degrees at B. These periodicsignals are independent of the line-of-sight angles, and are identicalfor all three targets. After crossing the semi-transparent area 74, thetarget images enter the wide sector 70 of parallel lines. The lines 72are intercepted, producing pulse sequences 86, the counts of which areproportional to the radial distances of the targets from the center. Thetarget farthest away from the center of the reticle, corresponding tothe circular trace 78 on the reticle T, produces the pulse sequence 86shown in FIG. 7(A). The target associated with the circular trace 80produces the pulse sequence 86 shown in FIG. 7(B). The target nearest tothe center of the reticle, corresponding to the circular trace 82,generates the pulse sequence 86 shown in FIG. 7(C).

If the target image is centered on the reticle, which means that theprojectile axis and the target line-of-sight are coincident, no signalswould be generated by the reticle, indicating that no correction to theprojectile course is required. However, if the target deviates from thecenter of the reticle, the parallel lines 72 will generate a series ofpulses, indicating that the projectile is drifting away from itsintended course. As the projectile farther deviates from the target, thenumber of pulses generated will increase, indicating greater coursecorrection. The discontinuity between the first and second series ofpulses advantageously provides a reference point for firing a divertthruster to correct the trajectory of the projectile.

Another embodiment of a reticle W is disclosed in FIG. 8. The reticle Wis similar to reticle T, except that it does not have the blank areas 74and 76. Its operation is the same as reticle T.

Yet another embodiment of a reticle Y is disclosed in FIG. 9. Thereticle Y comprises a plurality of alternating light transmitting andopaque structures 88 and 90, each of which is thinner at ends 92 and 94and gradually thickens toward the other ends 96 and 98. The structures88 and 90 are closer together at one area of the reticle and furtherapart at another area. The structures 88 and 90 can be light absorbingand light reflecting, respectively, when working in some part of thespectrum, such as the infrared region.

When the reticle Y is rotated about its center 100 due to the spinningof the projectile, a circle 102 traced by an image of a target willcross the structures 88 and 90, generating a plurality of pulses at thedetector 24. The pulses will be higher frequency when the imagetraverses the region 104 where the structures 88 and 90 are closertogether and lower frequency in the region 106 where the structures arefarther apart. This change in frequency occurs for each rotation of thereticle and is detectable to provide an angular reference. It is seenthat the width of the structures 88 and 90 vary in a unique,distinguishable, unambiguous, and singly periodic fashion during therotation to provide a reference point for sequencing the divertthrusters used to correct the trajectory of the projectile. The numberof pulses generated corresponds to the radial distance of the image fromthe center. The farther away the image is from the center, the greaternumber of structures similar to 88 and 90 that are traversed.

The electronic extraction of guidance signals is illustrated using thesignal generated by the reticle T (FIG. 6). An exemplary processingcircuit 108 is disclosed in FIG. 10. The photodetector signal isamplified by amplifier 110 and applied to a phase-lock loop circuit 112,which produces a steady clock signal at the frequency of theintersection with the alternating reticle structures and a pulse signalat the instant of the phase discontinuity. The clock frequency and thephase discontinuity signal are used for the sequencing of the divertermatrix 28 and the thruster firing, respectively. Furthermore, they areused together for the extraction of the line-of-sight angles by means ofa shift register 114 and a pulse counter 116.

The phase-lock loop block 112 is broken down into its elements, as bestshown in FIG. 11. The amplified seeker signal is applied via a band-passfilter 118, together with the output of a voltage controlled oscillator(VCO) 120, to a phase detector 122 via a divide by N counter 121, whereN is the number of elements 46 in the divert thruster 28. The phasedetector 122 measures the instantaneous phase difference of the twosignals, and via an integrator 124 determines the frequency difference,and tunes the VCO frequency so that it matches the input frequency. Theinstantaneous phase jump is available at the output of the phasedetector 122, but does not influence the VCO tuning. The VCO frequencyis thus phase-locked to the input signal.

Another exemplary circuit is disclosed in FIG. 12 to illustrate theextraction of the long pulse from the reticle signal generated by thereticle R (FIG. 1). The long pulse provides the unique, unambiguous,detectable and singly periodic signal for each rotation of the reticle.Preprocessed signal from the detector, shown in FIG. 13A, is input tothe circuit at 126. Output signal at 128, shown in FIG. 13B, is input toa low-pass filter, generating a signal shown in FIG. 13C at 130. Theoutput signal from the differential amplifier at 132 is shown in FIG.13D.

The various exemplary circuits illustrated herein may be implementeddigitally, wherein the signal from the reticle is digitized by ananalog/digital converter and processing is done by a microprocessorprogrammed with appropriate algorithms simulating the operationsperformed by the analog circuits.

The above reticle embodiments are representative of a large number ofreticle configurations which could yield similar signal output under thesame circumstances. All these reticles provide two commoncharacteristics which essentially determine their usefulness for guidingspinning projectiles, namely:

(1) A target image moving on such reticle about an optical axis in acircular pattern will produce reticle line crossings the number of whichis a monotone increasing (but preferentially linear) function of theradius of the circular path of the image.

(2) The pulse lengths and/or the interstitial time periods betweenpulses vary in a unique, distinguishable, unambiguous, and singlyperiodic fashion during the spin cycle. Same as the change in pulselength from a maximum to a minimum, any other distinct, predominant, andreadily detectable feature of the signal would be equally useful, if itbehaved similarly for every completion of the full circle (360 degreesrotation).

The reticles disclosed herein may be implemented on any suitablesubstrate, such as the refractive and reflective embodiments discussedabove that will permit light or infrared radiation to pass through or bereflected therefrom and be detected by a photodetector. Other materialsmay be used, depending on the specific radiation emitted by or reflectedfrom the target. The reticles may even be deposited directly on theactive surface of a photodetector chip. The timing, sequencing andfiring circuits for the diverters may also be implemented on the samechip.

The present invention provides a guidance seeker that has relatively lowcost and small size realization, making it particularly suitable forvery small caliber spinning projectile applications.

While this invention has been described as having a preferred design, itis understood that it is capable of further modification, uses and/oradaptations following in general the principle of the invention andincluding such departures from the present disclosure as come withinknown or customary practice in the art to which the invention pertains,and as may be applied to the essential features set forth, and fallwithin the scope of the invention or the limits of the appended claims.

What is claimed is:
 1. A reticle for a guidance seeker, comprising: a) asubstrate having a center of rotation; and b) an alternating pattern oflight modulating structures disposed on said substrate along a 360degree path about said center of rotation such that when an image of atarget formed on said substrate moves along said path said imagegenerates a plurality of pulses corresponding to a number of saidstructures crossed by said image, a number of said plurality of pulseschanging as said image moves outward radially from said center ofrotation; wherein said plurality of pulses form guidance control signalsincluding a unique, unambiguous and singly periodic signal for eachrotation of said substrate to provide an instantaneous target locationin polar coordinates centered about said center of rotation, and whereinsaid polar coordinates are indicative of a line of sight angle betweensaid center of rotation and a target line of sight for determiningcourse correction and include a polar angle component in reference tosaid center of rotation and said image for determining timing anddirection for applying a vector force along a line through said imageand said center of rotation such that said line of sight angle isreduced.
 2. A reticle as in claim 1, wherein said structures includelight transmitting and opaque lines.
 3. A reticle as in claim 1, whereinsaid structures include light reflecting and light absorbing lines.
 4. Areticle as in claim 1, wherein said structures include chevron-shapedlines.
 5. A reticle as in claim 1, wherein said structures includeconcentric arcs.
 6. A reticle as in claim 1, wherein said structuresinclude radial lines and parallel lines.
 7. A reticle as in claim 1,wherein said structures include an area on said substrate adapted togenerate said unique, unambiguous and singly periodic signal.
 8. Areticle as in claim 7, wherein said area is light transmitting.
 9. Areticle as in claim 7, wherein said area is light absorbing.
 10. Areticle as in claim 1, wherein said substrate includes a first areawhere said structures are grouped closer together and a second areawhere said structures are grouped farther apart along said path.
 11. Amethod for generating a guidance signal for a projectile spinning abouta spin axis, comprising the steps of: a) providing a reticle securedstationary with respect to the projectile, the reticle having a patternof alternating light modulating structures disposed along a pathcoinciding with the spin axis; b) allowing the reticle to rotate withthe projectile about the spin axis; c) forming an image of a target onthe reticle; d) generating a plurality of pulses from the relativemotion of the target image on the reticle as the image crosses thealternating light modulating structures for each rotation of thereticle, the plurality of pulses being indicative of a line of sightangle between the spin axis and a target line of sight for determiningcourse correction, whereby an absence of the plurality of pulsesindicates that the projectile is on course; e) extracting a unique,unambiguous and singly periodic signal from the plurality of pulses toprovide an instantaneous target location in polar coordinates centeredabout the spin axis for each rotation of the reticle; and f)determining, from a polar angle component of the polar coordinates,timing and direction for applying a vector force through a center ofmass of the projectile along a line through the image and the spin axissuch that the line of sight angle is reduced.
 12. A reticle for aguidance seeker, comprising: a) a substrate having a center of rotation;b) a plurality of alternating light modulating structures disposed onsaid substrate; c) said plurality of alternating modulating structuresbeing disposed on said substrate such that an image of a target tracinga path on said substrate about said center of rotation crosses a greaternumber of said structures as a radial distance of said image from saidcenter of rotation increases; and d) a width of said structures vary ina unique, distinguishable, unambiguous and singly periodic fashion alongsaid path to provide an instantaneous target location in polarcoordinates centered about said center of rotation, wherein said polarcoordinates are indicative of a line of sight angle between said centerof rotation and a target line of sight for determining course correctionand include a polar angle component in reference to said center ofrotation and said image for determining timing and direction forapplying a vector force along a line through said image and said centerof rotation such that said radial distance of said image from saidcenter of rotation is reduced.
 13. A reticle as in claim 12, whereinsaid structures include light transmitting and opaque spaces.
 14. Areticle as in claim 12, wherein said structures include light reflectingand light absorbing spaces.
 15. A reticle for a guidance seeker,comprising: a) a substrate having a center of rotation; b) a pattern ofa plurality of alternating opaque and light transmitting lines disposedalong a 360 degree path about said substrate such that an image of atarget moving on said substrate generates a plurality of pulsescorresponding to a number of lines crossed by said image, said pluralityof pulses increasing as said image moves outward radially from saidcenter of rotation; and c) a blank area on said substrate such that atime interval for said image to traverse said blank area issubstantially greater than a time interval for said image to traversesuccessive opaque lines; wherein said plurality of pulses form guidancecontrol signals including a unique, unambiguous and singly periodicsignal for each rotation of said substrate to provide an instantaneoustarget location in polar coordinates centered about said center ofrotation, and wherein said polar coordinates are indicative of a line ofsight angle between said center of rotation and a target line of sightfor determining course correction and include a polar angle component inreference to said center of rotation and said image for determiningtiming and direction for applying a vector force along a line throughsaid image and said center of rotation such that said line of sightangle is reduced.
 16. The reticle as claimed in claim 1 wherein anamount of force of said vector force is proportional to a radialdistance component of said polar coordinates such that a greater amountof force is applied as said radial distance component increases.
 17. Themethod as claimed in claim 11 wherein an amount of force of the vectorforce is proportional to a radial distance component of the polarcoordinates such that a greater amount of force is applied as the radialdistance component increases.
 18. The reticle as claimed in claim 12wherein an amount of force of said vector force is proportional to saidradial distance such that a greater amount of force is applied as saidradial distance increases.
 19. The reticle as claimed in claim 15wherein a greater amount of said vector force is applied as said imagemoves outward radially from said center of rotation of said substrate.